CASH-STRAPPED Ireland is calling in an unlikely favour from the Queen to help out her nearest neighbour in its hour of need.

Tourism chiefs have asked the monarch if she will turn Buckingham Palace green for St Patrick's Day in a gesture that would signal another milestone in relations across the Irish Sea.

Some of Earth's most famous sights - including the Pyramids and Rio de Janeiro's Christ the Redeemer statue - are to be illuminated emerald on the national day of celebration in a bargain-basement bid to bring more visitors to Ireland.

But despite the Queen's ground-breaking visit to the Republic, she has not yet given the green light for a change of colour at her world-famous official residence in London.

Niall Gibbons, chief executive of Tourism Ireland, said they were still awaiting a response from Buckingham Palace.

"I have written to the private secretary to the Queen, but we haven't had a reply yet," he said.

"We wrote a couple of months ago, but it is a dialogue that is in progress. I wouldn't be putting any pressure on people."

To help their case, the tourism agency is expected to unveil details in the coming weeks about the previously unknown Irish roots of the Duchess of Cambridge.

"We have actually traced Kate Middleton's Irish ancestry back as well. We have a report on it," said Mr Gibbons.

"We have an authenticated connection, with all the certificates and everything."

Other international attractions going green on March 17 include the Sydney Opera House, Niagara Falls, the Leaning Tower of Pisa, Burj al Arab in Dubai, Table Mountain in South Africa, New York's Empire State Building and Berlin's TV Tower.

Ireland's tourism minister Leo Varadkar revealed an ambitious list has been drawn up of other globally-renowned structures and buildings which overseas Irish diplomats are targeting as part of the global greening initiative.

"It does arise that some of the ones we really want have asked for money and we can't justify spending large amounts of money," he said.

The entire scheme, which will also see the "greening" of New Zealand's Sky Tower, Vienna's Burg Theatre and the Prince's Palace in Monaco, is costing about 34,000 euro (£29,400).

Ireland is turning to its strong identity abroad, not least in the sprawling 70 million-strong Irish diaspora, to help lift it out of an unprecedented economic crash.

It was hoped the visit of the Queen and Duke of Edinburgh to Ireland two years ago - the first by a British monarch to the Republic since 1911 - would provoke a rise in the number of holidaymakers from the UK.

But despite attempts to tap into the trip, figures have so far been disappointing with visitor numbers down 3% last year.

"The British market is very difficult," admitted Mr Varadkar, who blamed the UK's own weak economy.

"Fewer British people travelled abroad last year than did 10 years ago, which is extraordinary if you think about it.

"And we still have a perception that Ireland is an expensive place to visit. Now, all the research we have shows that this is improving and British people now coming to Ireland are going back and saying that Ireland isn't that expensive after all, hotels and accommodation in particular are very good value.